I have the upgraded battery and it indeed does not lose charge while the player is off.

I have the same but there can always be a bad one here or there, such is the nature of our imperfect world. Like most, I don't like to be the one that gets the bad apple. :^) HiFiman is good at responding though.

What's wrong with the cover? Mine wouldn't latch and I discovered that the inner piece of metal that hangs down on the cover was bent too far towards the edge. I opened up the gap between it and the edge and then the slide worked correctly and I could close the case again. I thought it needed to be closer at first but then realized it was already to close, the gap was too narrow.